1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, particularly to a semiconductor integrated circuit having a fuse which can be blown out by light irradiation.
2. Description of the Related Art
Recently the number of elements in a semiconductor integrated circuit represented by DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory) is remarkably increasing and an unexpected defect in fabrication steps deteriorates the yield inevitably. To overcome the defect, those methods have been put into practice in which a redundant circuit is provided in a chip circuit and a defective memory cell in a main memory is replaced with a spare memory cell to make the whole chip circuit acceptable. One of the methods is laser blowing.
Laser blowing generally uses a fuse as an element for switching a main memory to a spare memory cell. FIG. 13A is a top view of a conventional fuse whose major constituent is aluminum and FIG. 13B shows a section B-Bxe2x80x2 thereof.
Referring to the drawings, numeral 2 designates an interlayer insulating film disposed between a metal member 3 and a silicon substrate 1, numeral 4 designates a passivation film arranged above the metal member 3 and those insulating films are formed of silicon oxide or silicon nitride. The metal member 3 is comprised of aluminum or copper and an upper face and a lower face thereof are covered by barrier metal layers 9 (the upper portion functions as an anti-reflection coating) comprising Ti, TiN or the like. A fuse includes the metal member 3 and the barrier metal layers 9.
In general laser blowing uses a laser beam with a wavelength of 1.0 xcexcm to 1.4 xcexcm in infrared region. When the metal member 3 is irradiated with a laser beam 5, the energy of the laser beam 5 is mainly absorbed by the barrier metal member 9a (anti-reflection coating) covering the upper face of the metal member 3 from among the barrier metal layers 9 covering the upper and lower faces thereof. Absorption of the laser beam 5 rapidly elevates the temperature of the barrier metal member 9a and the metal member 3 warms up by conductive heat from the barrier metal layer 9.
When the metal member 3 heats up and changes rapidly its state from a solid to a gas via a liquid, a change of pressure occurring quickly at this occasion blows off the passivation film 4. Simultaneously, the metal member 3 is blown out and a blow phenomenon completes itself. The details of the blow phenomenon of the metal member 3 are described in Japanese Patent Laid-Open No. 208635/2000.
Now, speedy driving and single chip system are required in a semiconductor integrated circuit, and then lower resistance of a wiring member in use and multilayering of a chip have been in progress. From a view point of the lower resistance of the wiring, a copper wiring has been put into practice in place of an aluminum wiring of the conventional art. The change in the material and the structure of the semiconductor integrated circuit affects laser blowing and the following points are necessary to be mentioned.
In accordance with the multilayering of the chip, it is requested that the fuse is formed at a wiring layer disposed at as upper as possible. To perform narrowing of a wiring pitch and speed up of an operational frequency at the same time, the formation of a lower resistance becomes indispensable for the wiring layer disposed at upper layers of the chip. As a result, a thicker layer is used for the wiring layer.
Using the wiring layer disposed at the upper layer as the fuse layer, then, signifies not only a change in the fuse material to copper but also the thicker film of the fuse. The thicker film of the fuse reduces the transmission efficiency of the laser beam to the fuse to thereby make laser blowing more difficult.
Meanwhile, a copper fuse formed by a Damascene process, for example, not like a fuse formed of aluminum wiring layer, has a structure in which three faces (two side faces and bottom face) of the copper member is covered by barrier metal layers convenience of the process. That is, in the case of the normal copper fuse, the barrier metal member 9a is not formed at the upper face of the metal member 3.
Therefore, in the case of the copper fuse of the related art, laser beam irradiated for laser blowing is reflected almost wholly by copper at the surface of the fuse. As far as laser beam having the wavelength of infrared region is used, it is difficult to firmly carry out laser blowing.
The invention has been carried out in order to overcome the above-described problems and it is an object thereof to provide a semiconductor integrated circuit having a fuse which can be firmly blown out by laser beam with a wavelength of an infrared region, even when a copper wiring layer disposed at an upper stage of the chip is used as a fuse layer.
According to an aspect of the invention, there is provided a semiconductor integrated circuit comprising a wiring member formed on a main face of a semiconductor substrate, a fusing member connected to the wiring member and having a predetermined thickness, a light absorbing member for covering a bottom face and a side face of the fusing member, and an insulating member for embedding the fusing member and the light absorbing member therein, wherein a complex permittivity of the light absorbing member is provided with a real part smaller than that of the fusing member in absolute value and an imaginary part larger than that of the fusing member.
Further, according to another aspect of the invention, there is provided a semiconductor integrated circuit comprising a wiring member formed on a main face of a semiconductor substrate, a fusing member connected to the wiring member and having a predetermined thickness, a barrier member for covering a bottom face and a side face of the fusing member, a light absorbing member for covering at least a side face portion of the barrier member for covering the fusing member, and an insulating member for embedding the wiring member, the fusing member, the barrier member and the light absorbing member therein, wherein a complex permittivity of the light absorbing member is provided with a real part smaller than that of the fusing member in absolute value and an imaginary part larger than that of the fusing member.